A flush memory is limited the total number of times in which writing actions are allowed. As a result, a semiconductor disk device is limited the total number of times in which writing actions are allowed, as well. On an occasion in which an effort is used to write a piece of information in a semiconductor disk device in excess of the allowable maximum times, a writing error readily occurs and the semiconductor disk device becomes incapable of being written a piece of information therein any longer. Accordingly, a semiconductor disk device available in the prior art is to have a use's area and a reserve area in which a piece of information is written in the cases where the user's area is full.
Referring to FIG. 1, a process for writing a piece of information in a semiconductor disk available in the prior art will be described below.
1. Step 301
When a semiconductor disk device receives a write command from a host computer, the semiconductor disk device conducts a process for accepting the write command.
2. Step 302
The semiconductor disk device conducts a process for forwarding a datum from the host computer to the internal data buffer of the semiconductor disk device.
3. Step 303
The controller unit of the semiconductor disk device calculates a sector address of the semiconductor disk device in which the datum is written.
4. Step 304
The controller unit of the semiconductor disk device checks the status of the selected sector in which the datum is scheduled to be written, the selected sector corresponding to the sector address. In other words, a check is conducted to find if the selected sector is a capable sector.
5. Step 305
If the selected sector is determined to be an incapable sector, a replacement sector is calculated out of the reserve area.
6. Step 306
In the case where the selected sector is determined to be a capable sector, or after a replacement sector is selected in the former step, the process goes to the step 306 and the number of times in which data were revised previously for the selected sector or the replacement sector. In other words, a check is conducted to find if the number of times in which revisions were previously conducted is within the allowable extent or not.
7. Step 307
If the number of times in which revisions were previously conducted is in excess of the allowable extent, a process is conducted to register a replacement sector.
8. Step 308
In the case where the number of times in which revisions were previously conducted is within the allowable extent or after a process was conducted to register a replacement sector, a process is conducted to forward datum from the internal data buffer of the semiconductor disk device to the selected sector or the selected replacement sector.
9. Step 309
The number of the sector administration table, the number showing the number of times in which data were previously revised, is revised.
10. Step 310
A check is conducted to determine if the foregoing steps were repeated for times corresponding to the number of sectors directed by the host computer. The foregoing steps are repeated for times corresponding to the number of sectors directed by the host computer. When the foregoing steps have been repeated for times corresponding to the number of sectors directed by the host computer, the process goes to normal completion.
Even in the cases where the foregoing process for writing a piece of information in a semiconductor disk available in the prior art is employed, situation is same after all the reserve areas have been employed. In other words, on an occasion in which an effect is used to write a piece of information in a semiconductor disk device after all the reserve areas have been employed, a writing error readily occurs and the semiconductor disk device becomes incapable of being written a piece of information therein any longer. In this event, since a user does not have a means to previously know the life of a semiconductor disk device, such an incident suddenly occurs to cause a serious problem to keep security of data.
An improved concept is known in the prior art that in case where the number of times in which writing actions were previously conducted for a semiconductor disk device has exceeded a predetermined number or a type of threshold value, a waning signal is issued. Even if this improved concept is realized, no users are allowed to know the instant position until the number of times in which writing actions were previously conducted for a semiconductor disk device arrives at the predetermined number or the threshold value. Incidentally, since the users can not know how long or how many times he will be allowed to do writing actions for the semiconductor disk device after he is given the warning signal, the improved concept is still unsatisfactory to secure security of the data, because the improved concept is not necessarily user friendly.